By Agence France-Presse
Jakkrit Panichpatikum, 40, a pistol-shooting star who competed in the Beijing and London Olympics, was killed in October 2013 by an assassin riding pillion on a moped.
His colourful life and stormy relationship with his wife Nitiwadee Pucharoenyot regularly made the Thai tabloids, including allegations that he beat her.
Months before his death, Nitiwadee and her mother Surang filed a complaint to police alleging he had assaulted his wife.
During the police murder probe, Surang confessed to using a lawyer as a middleman to find two hitmen to kill Jakkrit because of the abuse.
But in a ruling on Monday, a Bangkok court acquitted the mother, deciding she had covered up for her daughter who commissioned the crime, defence lawyer Chamnan Chadit told reporters.
The court convicted Nitiwadee and the middleman and "ruled... that they will face the death penalty", he said, adding both pleaded not guilty.
The shooter and moped driver, who did not contest their charges, were given life sentences.
Although the death penalty exists on the Thai statute books it is rarely carried out.
The last time was in 2009 when two drug traffickers were put to death by lethal injection.